1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and driving method, and in particular to a transreflective type liquid crystal display apparatus and driving method, which is excellent particularly in moving image visibility and capable of realizing excellent display images without depending on ambient illuminance.
2. Description of the Related Art
A flat-panel display device represented by a liquid crystal display apparatus is characterized by light weight, thinness and low power consumption, and widely used as a display device in a personal computer, portable information terminal, television or car navigation system.
In the liquid crystal display apparatus, a plurality of pixels is arranged like a matrix, and light transmittance of each pixel is controlled, whereby images are displayed. Therefore, the liquid crystal display apparatus is available in transmissive, reflective and transreflective types according to light-use modes.
A transmissive type liquid crystal apparatus has a lighting device called a backlight in the rear of a display panel, and its light-transmission amount is controlled for displaying images. In this transmissive type liquid crystal display method, good images can be displayed even in dark places with less ambient light. However, in places with bright ambient light, like outdoors, brightness is insufficient and display visibility is lowered.
Contrarily, in a reflective type liquid crystal apparatus, ambient light around a display device is reflected inside a display panel, and the reflection amount is controlled, whereby images are displayed. Therefore, the reflective type is suitable for use in places with bright ambient light, like outdoors, but displayed images are difficult to recognize in dark places with less ambient light.
In a transreflective type liquid crystal apparatus, a reflective part to display images by reflecting ambient light and a transmissive part to display images by transmitting backlight light are provided in one pixel. Therefore, the transmissive display function and reflective display function are compatible, and excellent display is realized without depending on ambient illuminance (Jpn. Pat. Appln. KOKAI Publication No. 2005-62573).
In the field of liquid crystal televisions and cellular phones, attention has been given to an OCB mode (Optically Compensated Bend Mode) liquid crystal display panel, which has a quick LCD response required for displaying images, and is capable of realizing a wide viewing angle.
In the OCB mode liquid crystal display panel, it is necessary to transit the liquid crystal alignment from the splay alignment to the bend alignment when displaying images. Therefore, a relatively large electric field is applied to the liquid crystal when power is turned on. However, this liquid crystal alignment is characterized to reversely transit to the splay alignment even after once transited to the bend alignment, when a voltage-applied state in which the energy of the splay alignment and the bend alignment is lower than a competitive level, or a no-voltage-applied state is continued for a long time.
For prevention of the reverse transition from the bend alignment to the splay alignment, there is a known driving method which applies a large voltage to the liquid crystal for each frame for displaying a 1-frame image. For example, in a normally-white liquid crystal display panel, this voltage corresponds to a pixel voltage that becomes black display, and black display is inserted with a predetermined ratio. This is known as black insertion driving. Black insertion driving also mitigates the sense of afterimage that occurs in display of moving images, by discrete impulse response of luminance.